A liquid crystal display device includes a TFT substrate and a color filter substrate. The TFT substrate is configured such that pixel electrodes, thin film transistors (TFTs), and the like, are arranged in a matrix form. The color filter substrate is disposed opposite to the TFT substrate, in which color filters, and the like, are formed at locations corresponding to the pixel electrodes of the TFT substrate. A liquid crystal is interposed between the TFT substrate and the counter substrate. Thus, the liquid crystal display device forms an image by controlling the transmittance of light of the liquid crystal molecules for each pixel.
Liquid crystal display devices can be made thin and light weight, and are used in a wide range of applications. The liquid crystal does not emit light by itself, so that a backlight is provided in the back surface of a liquid crystal display panel to emit light. Fluorescent tubes have been used as a backlight for liquid crystal display devices having a relatively large screen such as TV. However, the fluorescent tube is filled with mercury vapor, imposing a heavy burden on the environment of the Earth. In particular in European countries, the use of such a fluorescent tube tends to be prohibited.
Under these circumstances, the fluorescent tube has been replaced by LED (light emitting diode) as a light source of the backlight. More and more liquid crystal display devices with LED light source are used every year also in large display devices such as TVs. The backlight of the liquid crystal display device requires a planar light source. However, the LED is a point light source. Thus, it is necessary to provide an optical system to form a planar light source by point light source LEDs.
JP-A No. 236701/2006 describes a configuration of a light guide panel formed directly under a liquid crystal display panel. The light guide panel includes concave portions arranged in line. Then, LEDs are placed in line in the concave portions. In other words, the configuration of JP-A No. 236701/2006 uses an optical component to diffuse light emitted from each LED from a side surface of the LED. A reflective sheet part of the optical component includes a diffuse reflection area 41DR having a diffuse reflection function, and a mirror reflection area 41R having a mirror reflection function. In this way, the light from the LEDs is intentionally diffused and reflected at a predetermined ratio, to improve the efficiency of the use of the light while preventing uneven brightness.
The technology described in JP-A No. 236701/2006 requires the reflective sheet part to include the diffuse reflection area 41DR having a diffuse reflection function, as well as the mirror reflection area 41R having a mirror reflection function. For this reason, the optical design is complicated. Further, when LED is used as a light source, heat generated by the LED is an important problem. However, there is no description of the problem of heat generation in JP-A No. 236701/2006.